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A Cambrian meraspid cluster; evidence of trilobite egg deposition in a nest site

David R. Schwimmer and William M. Montante
A Cambrian meraspid cluster; evidence of trilobite egg deposition in a nest site
Palaios (May 2019) 34 (5): 254-260


Recent evidence confirms that trilobites were oviparous; however, their subsequent embryonic development has not been determined. A approximately 6 cm (super 2) claystone specimen from the upper Cambrian (Paibian) Conasauga Formation in western Georgia contains a cluster of >100 meraspid trilobites, many complete with librigenae. The juvenile trilobites, identified as Aphelaspis sp., are mostly 1.5 to 2.0 mm total length and co-occur in multiple axial orientations on a single bedding plane. This observation, together with the attached free cheeks, indicates that the association is not a result of current sorting. The majority of juveniles with determinable thoracic segment counts are of meraspid degree 5, suggesting that they hatched penecontemporaneously following a single egg deposition event. Additionally, they are tightly assembled, with a few strays, suggesting that the larvae either remained on the egg deposition site or selectively reassembled as affiliative, feeding, or protective behavior. Gregarious behavior by trilobites ("trilobite clusters") has been reported frequently, but previously encompassed only holaspid adults or mixed-age assemblages. This is the first report of juvenile trilobite clustering and one of the few reported clusters involving Cambrian trilobites. Numerous explanations for trilobite clustering behavior have been posited; here it is proposed that larval clustering follows egg deposition at a nest site, and that larval aggregation may be a homing response to their nest.

ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 34
Serial Issue: 5
Title: A Cambrian meraspid cluster; evidence of trilobite egg deposition in a nest site
Affiliation: Columbus State University, Department of Earth and Space Sciences, Columbus, GA, United States
Pages: 254-260
Published: 201905
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 49
Accession Number: 2019-063788
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 plate, 1 table, sketch map
N34°37'00" - N34°58'60", W84°55'60" - W84°35'60"
Secondary Affiliation: Tellus Science Museum, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201933
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